The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
A vehicle includes an internal combustion engine that generates drive torque. An intake valve associated with a cylinder of the engine is selectively opened to draw air into the cylinder. The air mixes with fuel to form an air/fuel mixture that is combusted within the cylinder. An exhaust valve associated with the cylinder selectively opens to allow exhaust gas resulting from combustion to exit the cylinder.
A rotating camshaft regulates the opening and closing of the intake valve and/or exhaust valve. The camshaft includes cam lobes that are fixed to and rotate with the camshaft. The geometric profile of a cam lobe determines a valve lift schedule. More specifically, the geometric profile of a cam lobe controls the period that a valve is open (duration) and the extent or degree to which the valve opens (lift).
Variable valve actuation (VVA) technology improves fuel economy, engine efficiency, and performance by modifying valve lift and duration as a function of engine operating conditions. Two-step VVA systems include variable valve lift mechanisms, such as hydraulically-controlled, switchable roller finger followers (SRFFs). A SRFF associated with a valve (e.g., the intake or exhaust valve) allows the valve to be opened in two discrete lift states: a low lift state and a high lift state. Valve lift is increased during operation in the high lift state.
A control module selectively transitions the SRFF mechanism between the high and low lift states. In other words, the control module controls which camshaft lobe will used to control opening and closing of the associated valve. For example, the control module may transition all of the SRFF mechanisms of the engine to the high lift state when the engine speed is greater than a predetermined speed, such as approximately 4,000 revolutions per minute (rpm).